Electric arc torch



Jan. 26, 1965 z, FONBERG 3,167,633

ELECTRIC ARC TORCH Filed May 7, 1962 Z ya/wu/vrfiZA ama ZNVENTOR.

United States Patent 3,167,633 ELECTRTC ARC TQRQ I Zygmunt Fonberg, Lebanon, NH asslgnor to Thermal Dynamics Corporation Filed May 7, 1962, Ser. No. US$60 4 Claims. (El. 219-75) My invention relates to electric arc torches of the general type employing plasma forming gases, and relates more particularly to improvements providing better means for igniting or initiating the main arc in such torches.

It has been common practice to initiate the main arc in electric torches by using, in addition to the main power supply, a source of high frequency high voltage electric energy. Such an approach is discussed, for example, in US. Patent No. 2,960,594, issued November 15, 1960. The voltage of the high frequency source is suflicient to form a pilot arc. This are produces an ionized conducting path for establishing the main arc. The main arc is then, in accordance with usual practice, swept to the center of an arc passage by the plasma forming gas.

The primary advantage of my invention is the simplification of the power supply for electric arc torches. I have provided means for initiating the main arc without the assistance of a high frequency source. Thus it is now possible to eliminate that portion of the power supply which has heretofore been necessary.

Another method of starting arcs (infrequently used) is to provide a conductor across the electrodes momentarily. This is hazardous for the operator and often damages one or both electrodes.

The novel features and advantages of the present invention will become apparent from the following description and accompanying drawings in which:

FIGURE 1 is a longitudinal cross-section of an electrode, insulator, and torch nozzle assembly; and

FIGURE 2 is a plan view of the insulator element and nozzle of FIGURE 1.

Referring to FIGURE 1, a torch is shown having a nozzle 3 and cathode 4, separated by an insulator 5. The insulator 5 may act as a swirl ring and is thus provided with tangential grooves 7 (FIGURE 2) to create a gas vortex flow through the nozzle 3. This mechanism is fully described in US. Patent No. 3,027,446, issued March 27, 1962, to James A. Browning.

I provide a layer of semi-conductive material such as graphite in the form of an annulus 6 on the surface of the insulator 5. The graphite is capable of being easily brought to incandescence and becomes volatile when an electric current is passed through it. A plurality of vertical strips 8 are arranged on the inner wall of the aperture in the insulator 5. The strips 8 are also of graphite or similar material and, when the torch is assembled as in FIGURE 1, it will be seen that the annulus 6 contacts the cathode 4, while the strips 8 run across the insulator and contact the anode nozzle 3.

A suitable power supply It) is employed to furnish elec trical energy to the torch. As shown, the cathode 4 acts as the negative or electron emitting electrode while the nozzle 3 forms the anode. It should be noted here that the power supply 1% need only supply the main are, no separate high frequency starter being required.

Upon closing of a switch 11, electric current passes from cathode to anode through strips 8 which act as resistive elements. The material of the anulus 6 and the strips 8 quickly come to incandescence. At the same time, a suitable plasma-forming gas is introduced under pressure and is flowing through the tangential grooves 7. This gas, or a portion of it in the proximity of the incandescent material becomes at least partially ionized,

thus providin a path for the establishment of the main are.

The gas vortex thereupon sweeps the arc to substantially the center of the nozzle. The continuing flow or" cool gas cools the strips 8 and stabilizes the are along the axis of the nozzle as desired. The torch then continues to operate in a conventional manner.

For repeated starting of the are I prefer a plurality of connections represented by the st ps 3, of which four are shown by way of example. he least resistant strip will usually burn or vaporize soonest, but remaining strips will serve for following starts. Since the action of the strips is only momentary, I have found that four or live such connections will provide numerous starts.

In special cases, a small amount of radioactive substance, such as strontium 90 or thorium, may be incorporated in the substance used to form the strips 8. The emission of beta particles and other radiation ionizes the gas introduced to the torch and thus facilitates the arc strining process.

The great advantage of my invention is its simplicity and safety when compared with presently accepted methods of starting arc torches. Although I provide a plurality of strips, it is also feasible to coat the inner surface of the aperture in the insulator 5 in its entirety. Gradually, paths in this coating are vaporized away, but not before many starts have been achieved. Where a single start-up is required, as for example in an experimental set-up, a single graphite line will sufiice.

While I have described a specific embodiment of my invention for illustrative purposes, modifications within the spirit and scope of the appended claims may occur to those skilled in this art.

I claim:

1. A plasma arc torch comprising a first electrode, a nozzle-like second electrode, a ring shaped insulator between said electrodes, a coating of conductive material on the inner surface of said insulator and joining said electrodes, means for supplying an electric current to pass between said electrodes through said material, said same means eing capable of supporting an are between said electrodes, and means for gas-stabilizing such are away from the inner surface of said insulator.

2. The method of striking an arc in an electric arc torch having an insulator with a central opening therein separating the electrodes of said torch; comprising coating the inner surface of the central opening in said insulator with resistive material, passing an electric current be tween said electrodes and through said material to heat same, providing a flow of gas through said insulator and over said material thereby creating a zone of ionization in the vicinity of said heated material to provide a path for the striking of an are between said electrodes, and gas-stabilizing said are away from the surface of said insulator after striking.

3. A plasma arc torch according to claim 1 in which the said conductive material is in the form of a plurality of strips joining said electrodes, said strips being of differing conductivities.

4. A plasma arc torch according to claim 1 in which said conductive material is composed of graphite.

References Cited by the Examiner UNITED STATES PATENTS Re. 25,088 11/61 Ducati et a1. 219- 1,002,721 9/11 Mathers 219121 2,829,235 4/58 Blink et al. 219--99 FOREIGN PATENTS 761,504 11/52 Great Britain.

RICHARD M. WGOD, Primary Examiner. 

1. A PLASMA ARC TORCH COMPRISING A FIRST ELECTRODE, A NOZZLE-LIKE SECOND ELECTRODE, A RING SHAPED INSULATOR BETWEEN SAID ELECTRODES, A COATING OF CONDUCTIVE MATERIAL ON THE INNER SURFACE OF SAID INSULATOR AND JOINING SAID ELECTRODES, MEANS FOR SUPPLYING AN ELECTRIC CURRENT TO PASS BETWEEN SAID ELECTRODES AND THROUGH SAID MATERIAL, SAID SAME MEANS BEING CAPABLE OF SUPPORTING AN ARC BETWEEN SAID ELECTRODES, AND MEANS FOR GAS-STABILIZING SUCH ARC AWAY FROM THE INNER SURFACE OF SAID INSULATOR. 